The three-dimensional structure of a number of enzymes are to be determined at atomic resolution using X-ray crystallography. Subsequent studies of complexes with substrate should then be informative of the mode of catalysis and give an understanding of the successive conformational changes during each turnover of these enzymes. Comparison of functionally related enzymes can then differentiate between those properties specific and those which are common, and therefore important, to the overall class of enzymes. Current work in this laboratory concerns itself with substrate and coenzyme complexes of lactate dehydrogenase and glyceraldehyde-3-phosphate dehydrogenase and with isozyme differences of lactate dehydrogenase. In addition structural investigations of catalase, phosphoglucomutase and quinolinate phosphoribosyltransferase are well on their way.